A database management system, or DBMS, is software that stores, retrieves and updates files from a centralized database. It acts as an intermediary between programs and the database, and allows multiple users or programs to access a data file at once. However, reliability and efficiency issues in larger networks prompted the implementation of a distributed database management system, or DDBMS, in which data files and processing functions are managed through several sites on a computer network.
Data and Process Distribution
In a centralized database, a DBMS can be implemented as a single process, single data scenario -- or SPSD -- in which one computer is linked to the host DBMS to retrieve data. A client/server DBMS can also be integrated as a multiple process, single data network -- called MPSD -- to allow more than one computer to access a single database.
Larger corporations may require an enterprise database to support many users over multiple departments. This would require the implementation of a multiple process, multiple data scenario, or MPMD, in which many computers are linked to a fully distributed client/server DDBMS.
The DDBMS offers more reliability by decreasing the risk of a single-site failure. If one computer in the network fails, the workload is distributed to the rest of the computers. Furthermore, a DDBMS allows replication of data among multiple sites; data from the failed site may still be available at other sites. A centralized DBMS differs because a failed computer that houses the database will debilitate the entire system.
A DDBMS can support three levels of transparency to hide certain complexities from the user, effectively managing the database as if it were centralized. Fragmentation transparency, the highest level of transparency, divides the original database into fragments and disperses them throughout the DDBMS. Therefore, the user does not need to specify fragment names or locations to gain access. Location transparency only requires the user to know the names of the fragments. Local mapping transparency, the lowest level of transparency, requires the user to know the name and location of a fragment.
Adding a new site to a DDBMS is easier than in a DBMS. Expanding or modifying a DDBMS occurs on a local level, and does not significantly hinder the operations of the other sites. However, making changes to a DBMS can be time-consuming and complex, since the network is centralized.
The efficiency of a DDBMS is increased through data localization, which disperses data where it is most often needed to match business requirements. This increases the speed of data access, because the user only has to query a local subset of the database instead of the entire database.
- "Database Systems: Design, Implementation, and Management"; Peter Rob, et al.; 2007
- "Introduction to Database Management Systems"; Atul Kahate; 2006
- Photo Credit Jupiterimages/Photos.com/Getty Images